The invention relates generally to a yarn feeder for feeding yarn to a textile machine, and more particularly, to a yarn feeder for feeding at least one yarn to a textile machine having a base support on which at least one lever can be pivoted around a horizontal pivot axis with an end remote from the pivot axis is in contact with the yarn under the force of its own weight.
Devices for monitoring whether yarn running into or out of a yarn feeder is proper, and whether the yarn delivered by the yarn feeder is provided in the correct amount or with the correct tension, often are provided on yarn feeders. In both cases hoop-shaped levers often are provided, which are pivotably seated on the yarn feeder and with an outer end resting on the yarn.
Such a yarn feeder, for example, is known from U.S. Pat. No. 5,860,298. The yarn feeder has a yarn feeding drum fastened on a vertical shaft and arranged in a yarn delivery path. Yarn feeler levers, which extend downwardly and in oblique fashion and rest with their free ends on the yarn, are arranged in the yarn delivery path upstream and downstream of the yarn feeding drum. If the yarn breaks, or too large an amount of yarn is present, the levers pivot downward under the force of their own weight and in the process actuate switches, which for example can be used for stopping the downstream-located textile machine.
The levers are pivoted under the force of their own weight. This must be a minimum weight in order to assure a dependable pivot movement, even if the yarn feeder is subjected to a certain amount of soiling in the course of the actual operating conditions. On the other hand, this results in increased friction at the yarn guide lever, which can be disadvantageous in particular in connection with thin and/or delicate yarns. If a particularly low yarn tension is desired, problems arise from too large a contact force, particularly because the yarn feeler lever tensions the yarn. The minimal yarn tensioning force must be great enough for the yarn to lift the yarn feeler lever.
Based on the foregoing, it is the object of the invention to provide a yarn feeder with a feeler lever that overcomes the foregoing problems and which is particularly adapted for use in controlling the feed of thin and delicate yarns.
In accordance with the invention, the lever, which is pivotably seated on the base support, is connected with a relief device, which reduces the weight of the lever by means of a spring force in at least a portion of its pivot range. Thus, the relief device enables the lever to rest on the yarn with a comparatively reduced force. By means of such device it is possible to reduce the friction between the yarn and the respective location of the lever. Moreover, it is possible to monitor even relatively thin yarn and/or to operate at reduced yarn tension.
Preferably the reduction of the weight of the lever is a function of the pivot angle. It is possible in this way to realize a deflection-dependent contact force on the yarn, which depends on the deflection angle of the lever in a non-linear manner. This can increase the triggering dependability, even if the yarn feeder is subjected to soiling.
Spring elements for generating a force which counters the weight permit a weight reduction without causing a noticeable increase in the moment of inertia of the lever, so that the latter can rapidly respond to a yarn break or decreasing yarn tension.
Wear-reducing ceramic elements can be arranged on the yarn feeler element. The weight relief compensates their weight at least partially. The service life of the elements which are in contact with the yarn can thereby be increased by the ceramic elements.
Preferably the spring element acts on the lever by means of a lever arm of such a type, that a neutral point is provided in the pivot range, wherein the spring element does not introduce a torque into the lever. The sign or direction of the torque is reversed in this neutral point, so that the spring element switches from a weight relief to an additional weight. This can increase the switch-off dependability.
Preferably the spring element is part of an electrical switch, so that no additional switch actuation forces need be provided. The force generated for the weight relief is also the switch-off force. This has the significant advantage that the full (not relieved and reduced) weight of the lever is available for actuating the switch, although the lever has been relieved of the weight from the viewpoint of the yarn.
For example, the spring element can be in the form of a U-shaped spiral spring. In addition, the latter can advantageously be used as a switching element. If the spiral spring has comparatively long legs, i.e. the legs are longer than their distance from each other, the spiral spring element is pivoted out relatively strongly, even with a small pivot movement of the lever. It thereby can be used as a switching member of a switch, wherein good and clearly defined switching points are provided because of the possible gearing, i.e. the comparatively greater pivot movement of the spiral spring in comparison with the pivot movement of the lever.